This invention relates to a superconductive excitation winding for the rotor of a turbogenerator, and more particularly to apparatus for maintaining a thermally insulating vacuum in the rotor.
A turbogenerator with a superconductive excitation winding and with rotating cryostats is described in an article "Turbogenerators with superconducting field coils" Bull. ASE 64 (1973) of August 17, 18, pages 1040 and following. At page 1043 of this publication, a turbogenerator is illustrated and described in which the excitation winding is cooled by liquid helium. The inner rotor which carries the excitation winding is arranged inside an outer cylinder. A high vacuum is produced in the space between the cylinders. The mounting of the inner rotor and the transfer of the torque to the shaft ends, which are at room temperature, is accomplished by thin wall portions which are cooled also with helium gas. A thin radiation cylinder is mounted in the space between the inner rotor and the outer cylinder to serve as an additional electro-thermal shield. The radiation cylinder also absorbs the heat radiated by the outer cylinder and reduces any remaining magnetic fields which penetrate the outer attenuating cylinder to a value that can be tolerated by the superconductor.
At the non-driven side of the shaft, there is provided a helium transfer unit with slip rings and lines supplying the excitation current which are cooled within the shaft by helium gas. In order to maintain the insulating vacuum, an external pump system is connected with the vacuum chambers of the rotor by means of rotating vacuum seals which must be designed and manufactured to close tolerances. However, these seals are subject to failure due to wear and tear. The external pump system has a high energy consumption due to its relatively low efficiency and is also subject to malfunction.
It is an object of this invention to overcome the deficiencies of prior apparatus for maintaining a thermally insulating vacuum in a rotor of a turbogenerator with a superconductive exciting winding and to provide apparatus which is simple in design, reliable in operation and efficient.